Insects and other arthropods constitute over half of the living animal species on earth; they are important not only from a biological viewpoint, but as disease vectors, and as agricutural, forest, and household pests. Insects interact chemically with one another, with plants, with animal hosts, and with predators. This project is concerned with elucidating the chemistry of these interactions. For the arthropods themselves attention will be paid not only to glandular substances, but also to systemic components that may play important roles in arthropod defense and/or communication. Plants have been co-evoloving with insects for many millions of years, and the chemical relationships between these two groups of organisms are rich and interesting. Our work with plants will emphasize the isolation and characterization of new insect repellents, and the utilization of plant alkaloids as insect defensive agents and pheromone precursors. In all cases, new compounds with demonstrable biological activities will be isolated and characterized. Chemical syntheses will be carried out to confirm structures and to provide material for bioassays. The overall objectives of this work are to increase our understanding of natural regulatory mechanisms, and to provide the basis for new control techniques of disease vectors or other pests.